As both demand for and supply of televised content grows, customers and media providers are becoming increasingly involved with pay television services. Pay television or pay-TV refers to subscription-based television services, typically provided by both analog and digital cable and satellite, but also increasingly by digital terrestrial methods. Pay per view (PPV) services are similar to subscription-based pay TV services and in that one must pay to have the broadcast decrypted for viewing, but typically entail a one-off payment for a single or time-limited viewing. “Free” variants are free-to-air (FTA) and free-to-view (FTV), however FTV services are normally encrypted and decryption cards either come as part of an initial subscription to a pay TV service or can be purchased for a one-off cost.
Some pay television services utilize a set-top box. A set-top box is a device that enables a television set to receive and decode digital television (DTV) broadcasts. DTV set-top boxes are sometimes called receivers. In some implementations, set-top boxes additionally provide a user interface to the Internet. In the Internet realm, a set-top box is sometimes a specialized computer that can “talk to” the Internet—that is, it contains a Web browser and supports Internet protocols, such as TCP/IP. When performing network communications, the service to which the set-top box is attached may be through a telephone line or through a cable TV company; such a setup may enable interactive two-way services. Two-way services are combined with the broadcast feed and a return path, typically with a charge for access and /or for the interactive content offered. Content on offer includes movie, gaming, betting, shopping and banking services. This often requires a secure conditional access system and mutual authentication between the end user and the set-top box.
Conditional access systems are typically composed of two parts: the head-end part and the reception-end part. At the head-end, the digital content (including video, audio and data), to which the operator (or service provider) wishes to restrict access, is scrambled by a control word (CW) derived from a constantly changing pseudo-random binary sequence generator. It is desirable to protect this control word as well, and therefore it is oftentimes encrypted with a service key (SK). The encrypted control word is then packaged into so-called entitlement control message (ECM). Further, the service key is encrypted with an individual key (IK) supplied by the subscriber management system and is then packaged with entitlement data into entitlement management message (EMM). Finally, the scrambled content, entitlement control message, and entitlement management message are together broadcast in the same channel.
At the reception-end, the set-top box (STB) filters the entitlement management message and entitlement control message according to the parameters provided by the user's personalized smart card (SC) and then forwards these messages to smart card. The smart card then decrypts the entitlement management message using the individual key (here stored in the smart card) to get the service key and the entitlement data. After having passed the verification of the access entitlement, the smart card uses the service key to decrypt the encrypted control word and returns the control word to the set-top box so that set-top box will be allowed to descramble the scrambled content.
In such an implementation, the control word is very vulnerable to the link between smart card and set-top box. If the smart card transfers the control word in plaintext form to the set-top box, an attacker, instead of being forced to compromise the smart card, can simply obtain the control word by monitoring the interface between the smart card and set-top box. Further, the attacker can distribute the control word through other channels to unauthorized users so that they can also access the protected content without license. This is a serious threat to the security of such a conditional access system. Thus, the control word must be protected from this attack.
On the other hand, the absence of mutual authentication mechanism in such an implementation would allow a fake set-top box, for example a computer with a hacked smart card reader, to challenge smart card or a pirated smart card to be used on set-top box to access the protected content.
Because of the various limitations presented in traditional methods of pay television license control, there is a need for an improved technique that reduces the above mentioned drawbacks that exist in the conventional methods.